The conventional air fans used on high speed processors such as microprocessors that include metal spindles encounter many problems such as the airflow is not sufficient to disperse the growing amount of heat being generated, rotation speed is not fast enough, etc. Increasing the speed and airflow volume will result in shorter service life of the metal spindle. Therefore ceramic spindle has gradually replaced the metal spindle these days. The ceramic material is very hard and rigid, and can withstand wearing and high temperature. Thus the air fan rotation speed may increase to disperse heat as desired.
However, test process during fabrication shows that there are still problems in the design of the ceramic spindle remained to be resolved. For instance, the ceramic spindle is usually jointly formed with the fan by injection. The ceramic spindle generally has a smooth surface and a low friction coefficient, hence the centrifugal force occurred at high speed rotation of the fan tend to result in separation of the ceramic spindle from the air fan and incurs skid. To remedy this problem, one of the approaches is to increase the friction of the surface of the ceramic spindle so that it can be coupled with the air fan tightly during injection forming. The original purpose of using the ceramic spindle is to take the advantage of its greater hardness and rigidity. The embossing process is useless for the ceramic spindle since the ceramic spindle is very hard and rigid. Even if the embossing process is finally done and successfully created a rough surface to the ceramic spindle, it would be a very time and cost consuming which is not economical.
To solve the aforesaid problem, Applicant has disclosed a patent in ROC patent publication No. 517784 entitled “Ceramic spindle coupling structure for air fans”. In that patent, the ceramic spindle has one end coupled with a metal bushing having a greater friction coefficient. Referring to FIG. 2 of the above patent for an embodiment, the inner ring surface of the metal bushing is embossed by a machine to increase the friction coefficient. The outer surface of the metal bushing is embossed to increase the friction coefficient. Then the metal bushing is tightly coupled with the ceramic spindle. The metal bushing is coupled with the air fan by injection forming to become integrated. Hence the ceramic spindle may be tightly coupled with the air fan without breaking loose. Such a structure requires embossing on the inner ring surface and outer surface of the metal bushing by machining. It needs additional embossing operations for the metal bushing during fabrication process. Production cost is higher. There is still room for improvement.